Shielding Benchmark Calculations with SCALE/MAVRIC and Comparison with Measurements for the German Cask CASTOR® HAW 20/28 CG

Shielding / Special Issue on the 11th International Conference on Radiation Shielding and the 15th Topical Meeting of the Radiation Protection and Shielding Division (PART 3) / Radiation Protection /dx.doi.org/10.13182/NT09-A9320

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The purpose of this research was to make shielding benchmark calculations with the new Standardized Computer Analyses for Licensing Evaluation (SCALE) shielding sequence Monaco with Automated Variance Reduction Importance Calculations (MAVRIC) and compare with SCALE SAS4/MORSE calculations as well as dose rate measurements for the German storage/transport cask CASTOR® high active waste (HAW) 20/28 CG. MAVRIC with improved transport methodology is the successor of SAS4 and was released as part of SCALE version 6 in 2009. The new calculations with MAVRIC resolve discrepancies of results obtained with SAS4 in comparison to measured data. Cask areas with heterogeneous structures like trunnions and ducts are of special interest.

Based on dose rate measurements for neutron and gamma radiation on a CASTOR® HAW 20/28 CG cask and to extend our own shielding calculations done with the SCALE SAS4/MORSE sequence, the new SCALE shielding sequence MAVRIC/Monaco has been used for comprehensive calculations to treat problematic cask shielding regions like trunnion areas and ducts in the cask lid.

The calculations with the SAS4 sequence are carried out with SCALE v4.4a. The prerelease test version of the MAVRIC sequence was added to SCALE v5.1 for testing purposes. The dose rate measurements are carried out for a single CASTOR® HAW 20/28 CG cask in storage configuration. Loading plans are used for calculating the source strength and the spectra of the inventory.

Calculations with the new MAVRIC sequence and the typical SCALE group shielding library consisting of 27 neutron and 18 gamma groups for points on the surface at the cask at midheight and in front of the trunnions show results that are closer to the measured dose rates than the SAS4 calculations.

First dose rate calculations with the new SCALE shielding sequence MAVRIC are presented. They show a better agreement to the measured data than the SAS4 sequence, especially for more complex regions. The reason is the three-dimensional treatment of the variance-reduction parameters in the new MAVRIC sequence as opposed to the one-dimensional biasing treatment in SAS4.